A post by Eytan Bakshy on behalf of the “Facebook Data Science Team” notes that on March 26, as the US Supreme Court was beginning to debate same-sex marriage, the number of changes to profile picture was markedly up, with 2.7 million, or 120%, more than the previous Tuesday.

The headline on Brian Moylan’s post at Vice is a fair clue to his assessment: “The red marriage equality sign on your Facebook profile is completely useless”.

In terms of what it might achieve in swaying the Supreme Court, changing your avatar, writes Moylan, is about as influential as “wearing green on St Patrick’s Day”.

It’s nice to see so many people who want their gay friends to be spoiled brides just like all their straight friends, but you’re not doing anything. This is just another form of passive activism that isn’t advancing the cause. Do you know what would be helpful? Actually picking up a sign, heading down to the Supreme Court, and joining the throngs of protesters. Do you know what would be useful? Instead of just downloading an image and clicking a few buttons, going to the website of a gay rights organization (or any gay organization for that matter) and giving them some money so they can fight for gay civil rights on your behalf.

Although the Supreme Court justices might not be checking Facebook to tally up the red avatars before making a decision, a demonstration of solidarity like this one really could end up making an impact.

Human beings remain “susceptible to the powers of peer pressure, or social proof”, she writes. “Our friends, family, and the people around us exert strong influences on our attitudes and behaviour, whether intentional or not.”

We often respond more positively, says Tannenbaum, to the “descriptive norms” of such phenomena, than the “prescriptive norms” of lectures and polemics.

People look at an issue like marriage equality, and the first inclination is to set prescriptive norms. We should do something, the justices should rule a certain way, you should support a given cause. But based on everything that we know about our brains and their bafflingly strong desires to fit in with the crowd, the best way to convince people that they should care about an issue and get involved in its advocacy isn’t to tell people what they should do — it’s to tell them what other people actually do.

The odds that the HRC’s campaign, as wildly successful as it has been, will directly influence the decision of the Justices are nil, which speaks quite loudly to the limits of online activism: twenty million avatars are not twenty million people in the street. However, as Jeffrey Toobin wrote, as people and politics change, so does the Court. And online activism has shown, most notably through its role in the defeat of the controversial Stop Online Piracy Act last year, that maybe it can change people.